1. Field of the Invention
This invention concerns alpha-amino acid containing chemical mechanical polishing compositions and slurries that are useful for polishing substrates including multiple layers of metals, or metals and dielectrics.
2. Description of the Art
Integrated circuits are made up of millions of active devices formed in or on a semiconductor substrate such as a silicon semiconductor wafer. The active devices, which are initially isolated from one another, are interconnected through the use of multilevel interconnections to form functional circuits and components. Interconnection structures normally have a first level of metallization, an interlevel dielectric layer, a second level of metallization, and sometimes a third and subsequent levels of metallization. Interlevel dielectrics such as doped and undoped silicon dioxide (SiO2) and low-κ dielectrics are used to electrically isolate the different levels of metallization in a semiconductor substrate or well. The electrical connections between different interconnection levels are made through the use of metallized vias. U.S. Pat. No. 5,741,626, which is incorporated herein by reference, describes a method for preparing dielectric tantalum nitride layers.
In a similar manner, metal contacts are used to form electrical connections between interconnection levels and devices formed in a well. The metal vias and contacts may be filled with various metals and alloys including titanium (Ti), titanium nitride (TiN), tantalum (Ta), tantalum nitride (TaN), aluminum copper (Al—Cu), aluminum silicon (Al—Si), copper (Cu), tungsten (W), tungsten nitride, and combinations thereof. The metal vias and contacts generally employ an adhesion layer such as titanium nitride (TiN), titanium (Ti), tantalum (Ta), tantalum nitride (TaN), tungsten, tungsten nitride, or combinations thereof to adhere the metal layer to the dielectric layer. At the contact level, the adhesion layer acts as a diffusion barrier to prevent the filled metal and dielectric layers from reacting. Processes for manufacturing and/or CMP of vias are disclosed in U.S. Pat. Nos. 4,671,851, 4,910,155 and 4,944,836.
In a typical chemical mechanical polishing process, the semiconductor wafer is placed in contact with a polishing pad. The pad and table are rotated while a downward force is applied to the backside of the semiconductor wafer. An abrasive containing chemically reactive solution, commonly referred to as a “slurry,” is applied to the pad during polishing. The polishing process is facilitated by the rotational movement of the pad relative to the substrate as slurry is provided to the wafer/pad interface. Polishing is continued in this manner until the desired film thickness on the insulator is removed. The slurry composition is an important factor in the CMP step. Depending on the choice of the oxidizing agent, the abrasive, and other useful additives, the polishing slurry can be tailored to provide effective polishing to metal layers at desired polishing rates while minimizing surface imperfections, defects, corrosion, and erosion. Furthermore, the polishing slurry may be used to provide controlled polishing selectivities to other thin-film materials used in current integrated circuit technology such as titanium, titanium nitride, tantalum, tantalum nitride, tungsten, tungsten nitride, and the like.
Typically, CMP polishing slurries contain an abrasive material, such as silica or alumina, suspended in an oxidizing aqueous medium. For example, U.S. Pat. No. 5,244,534 to Yu et al. reports a slurry containing alumina, hydrogen peroxide, and either potassium or ammonium hydroxide that is useful to remove tungsten at predictable rates with little removal of the underlying insulating layer. U.S. Pat. No. 5,209,816 to Yu et al. discloses a slurry comprising perchloric acid, hydrogen peroxide and a solid abrasive material in an aqueous medium that is useful for polishing aluminum. U.S. Pat. No. 5,340,370 to Cadien et al. discloses a tungsten polishing slurry comprising approximately 0.1 M potassium ferricyanide, approximately 5 weight percent silica and potassium acetate. Acetic acid is added to buffer the pH at approximately 3.5.
U.S. Pat. No. 4,789,648 to Beyer et al. discloses a slurry formulation using alumina abrasives in conjunction with sulfuric, nitric, and acetic acids and deionized water. U.S. Pat. Nos. 5,391,258 and 5,476,606 disclose slurries for polishing a composite of metal and silica which include an aqueous medium, abrasive particles and an anion which controls the rate of silica removal. U.S. Pat. No. 5,770,095 discloses polishing slurries including a chemical agent and an etching agent selected from aminoacetic acid, and amidosulfuric acid along with an oxidizing agent. Other polishing slurries for use in CMP applications are described in U.S. Pat. No. 5,527,423 to Neville et al., U.S. Pat. No. 5,354,490 to Yu et al., U.S. Pat. No. 5,157,876 to Medellin, U.S. Pat. No. 5,137,544 to Medellin, and U.S. Pat. No. 4,956,313 to Cote et al.
There are various mechanisms disclosed in the prior art by which metal surfaces can be polished with slurries. The metal surface may be polished using a slurry in which a surface film is not formed in which case the process proceeds by mechanical removal of metal particles and their dissolution in the slurry. In such a mechanism, the chemical dissolution rate should be slow in order to avoid wet etching. A more preferred mechanism is, however, one where a thin abradable layer is continuously formed by reaction between the metal surface and one or more components in the slurry such as a complexing agent, an oxidizing agent, and/or a film forming agent. The thin abradable layer is then removed in a controlled manner by mechanical action. Once the mechanical polishing process has stopped a thin passive film remains on the surface and controls the wet etching process. In most cases, however, chemical mechanical polishing proceeds by some combination of these two mechanisms. Mechanical action can remove not only the surface film but also the metal underneath, with metal dissolution and passivation providing a needed control for the overall process: small metal particles are preferentially dissolved in the slurry, while some passivation of the remaining surface gives protection to the patterned metal against excessive dishing.
Ta and TaN are chemically very passive and mechanically very hard and thus difficult to remove by polishing. The use of a single slurry, which performs with a high Cu:Ta selectivity may demand prolonged polishing times for Ta, i.e., significant over polishing times for copper, during which there is significant dishing and erosion. As a result, there remains a need for CMP compositions and slurries that can be used successfully to polish multiple layer substrates at high rates and selectivities. There also remains a need for CMP compositions and slurries that can polish multiple substrate layers at similar or dissimilar rates and selectivites in order to improve planarization.